Gel-forming fabric composite

ABSTRACT

A method for the manufacture of a reinforced gel-forming fabric composite comprising a reinforcing layer and gel-forming fibre material is characterized in that the gel-forming fibre material in non-woven fabric form is needled into the reinforcing layer from one side so as to penetrate through the reinforcing layer and form a layer of gel-forming fibre material on both sides of the reinforcing layer. The resulting fabric finds use in a wound dressing.

FIELD OF THE INVENTION

The present invention relates to an improved method for making a fabriccomposite comprising, gel-forming fibre material, in particular alginatefibre material.

It is known to produce fabrics from gel-forming fibres, in particularalginate fibres, more particularly either calcium alginate orsodium/calcium alginate. These fibres and the fabrics produced from themhave the characteristic that when brought into contact with watercontaining certain ions, particularly sodium ions, they react to form agel. Gel-forming fibres such as alginate fibres are, therefore, veryuseful in the production of wound dressings. Similarly, fabrics madefrom carboxymethyl cellulose fibres are gel-forming in the presence ofwater and are also useful for wound dressings.

BACKGROUND ART

U.S. Pat. No. 5,674,524 describes and claims an alginate dressing whichis needle punched onto a non-alginate backing web so that fibres fromthe alginate layer penetrate into and are interlocked with the backingweb. In the fabric described in that specification there is clearly abacking layer on one side of the product which is a non-alginate layerand an alginate dressing on the front side of the product. All of thedescription is concerned with the penetration of the alginate fibresinto the backing layer to produce a continuous product. In column 5,lines 25 to 32, it is specified that a particular advantage of thealginate dressing containing a backing is the ease with which anadhesive strip can be placed on the backing and hold the alginatedressing in place. Because alginate becomes hydrocolloidal, i.e. gels,in an exudating wound the adhesive strip would become moist and easilydisassociated from the alginate dressing should the alginate materialhave penetrated the backing. Thus, the US patent is clearly directed toa two-layer structure in which the backing does not have alginate on itsexterior.

WO-A-99/67456 describes the formation of a three-layer structure for afabric composite comprising two outer gel-forming fibre layers whichsandwich a central core or reinforcing layer. The three-layer structureis produced by needling first and second webs of gel-forming fibre to atextile fibre scrim so as to produce a fabric with the gel-formingfibres on both sides. As described in Example 2 of WO-A-99/67456, thefabric composite can be made by laying up cross-laid, carded and needledwebs of a gelling fibre such as carboxymethyl cellulose on either sideof a spun-bonded fabric, typically a polypropylene fabric. The assemblyis then needled together to produce the fabric.

GB-A-1,394,742 discloses surgical dressing material comprising a layerof knitted alginic material adhered to one side of a layer of flexiblebacking material by damping followed by drying.

WO-A-90/01954 discloses a wound dressing comprising a wound contact padof a mixed salt alginate and a backing layer which may be bonded to thewound contact pad by adhesive.

U.S. Pat. No. 5,340,363 discloses a wound dressing comprising aswound-contacting surface a porous hydrophobic layer composed of anelastic net-like porous reinforcing component substantially completelyencapsulated by a soft and elastic hydrophobic gel such as silicone gelwhilst retaining the porosity of the net-like reinforcing component, sothat the layer includes openings which permit wound exudate to passthrough the hydrophobic layer to be absorbed in an outer absorbent layerattached to the hydrophobic layer.

U.S. Pat. No. 5,489,262 discloses a wound dressing containing a hydrogelmaterial in a gel-like phase adhesively bonded to a support layer whichis adhesively bonded to a backing layer.

WO-A-96/13282 discloses a wound dressing comprising a wound-contactinglayer having a positive effect on the healing of the wound, for examplean alginate layer, and a second layer of greater hydrophilicity than thefirst layer, for example an alginate or carboxymethyl cellulose layer.

DISCLOSURE OF THE INVENTION

We have now found that it is possible to provide what appears to be athree-layer structure, comprising a pair of gel-forming fibre layerssandwiching a central core or reinforcing layer, from just two layers ofmaterial. It has surprisingly been found that if a non-woven alginate orother gel-forming fabric, for example formed by non-woven carding andcross-folding, is needled onto a scrim central core or reinforcing layerit is possible for the non-woven alginate fabric to be needle punchedcompletely through the scrim central core or reinforcing layer so thatthe non-woven alginate fibre material appears on both sides of thereinforcing layer and the reinforcing layer becomes buried within thestructure. This gives the appearance of the scrim being centred andremaining virtually invisible on the face surfaces of the fabriccomposite. The scrim can be viewed from the edges of the composite buteffectively cannot be seen from the faces.

It is particularly surprising that this can occur with alginate fibresas gel-forming fibres given that alginate fibres are weak fibres andthey are punched completely through the centre scrim layer.

According to the present invention, therefore, a method for themanufacture of a reinforced gel-forming fabric composite comprising areinforcing layer and gel-forming fibre material, is characterised inthat the gel-forming fibre material in non-woven fabric form is needledinto the reinforcing layer from one side so as to penetrate through thereinforcing layer and form a layer of gel-forming fibre material on bothsides of the reinforcing layer.

The fabric composites made by the method of the invention aredifferentiated from those made from three layers as in WO-A-99/67456 bythe fact that, because the gel-forming fibre material is on only a firstside of the scrim reinforcing layer prior to needle punching, the twoapparent layers in the finished product have a single origin rather thanbeing initially separate.

The fabric composites are differentiated from known composites in whichgel-forming fibre material is needled into the first side of a web ofnon-gel-forming fibre as in U.S. Pat. No. 5,674,524 by the fact that thegel-forming fibres extend through the web of non-gel-forming fibre tocover the opposite side of that web and form a layer of gel-formingfibre material over it on both sides.

The fabric composites find use as wound dressings, where they can formthe wound contacting surface of the dressing.

The scrim central core or reinforcing layer may comprise any suitablewoven, non-woven or knitted fabric. When the fabric composite is to beused as a wound dressing the scrim may contain an anti-microbial agentor be medicated, for example using an anaesthetic such as lidocainehydrochloride.

In a preferred embodiment according to the invention when the fabriccomposite is to be used as a wound dressing, the scrim central core orreinforcing layer is sputtered or otherwise coated or impregnated withsilver prior to needling the alginate through the scrim layer.Particularly in this embodiment, the scrim is preferably a cellulosicfibre layer such as lyocell or a synthetic fibre layer such as nylon,polyester or polyethylene.

The scrim confers on the gel-forming fabric an increased level oftensile strength that ensures one-piece removal of the fabric compositefrom the wound site when it is used as a wound dressing. This isdifficult to achieve when gel-forming fibres are used, withoutreinforcement, particularly alginates, especially in bulky non-wovenform, which is the form giving maximum softness, conformability andabsorbency for wound dressings.

A number of benefits result from the invention. Firstly, one-pieceremoval of the fabric composite is ensured. Secondly, the strengthenedfabric is particularly useful as a cavity dressing in the form of atape, i.e. a narrow fabric, where the leaving behind of dressingmaterial might go unnoticed or else the material left behind might bedifficult to retrieve, at dressing changes. Thirdly, there is no contactbetween the scrim reinforcing layer and the wound whichever face of thefabric composite touches the wound, due to effect of the gel-forminglayer. Finally, the fabric can be formed as a lightweight fabric becauseit is formed using a single gel-forming web only.

The fabric according to the invention can be manufactured by a singlepass process through a single board needle loom, yet it gives theappearance of a structure manufactured by two passes, i.e. by needlingfrom top and bottom. There is no detrimental effect on absorbency.

The webs which may be used to produce the alginate layers includecalcium alginate or sodium/calcium (fast gel) alginate (basis weight70–200 gm⁻²). These are bonded to, for example, a lyocell woven gauzescrim (40 μm⁻²) by passing through a single board needle loom, with thealginate web as the top layer and the scrim as the bottom layer.Needling through the alginate web into the scrim is preferably carriedout using needles available from Foster Needles Limited, of Leicester,England, of the type 15×18×38×3RBA, F20 6-3B. The needle punch densityis preferably in the range of 40–200 ncm⁻², with a penetration of 4–15mm. Carboxymethyl cellulose may alternatively be used as gel-formingfibre.

The invention is further illustrated by the following Example.

EXAMPLE

A 50/50 sodium/calcium alginate was cut into 50 mm staple, openedthrough a Shirley Wheel opener, carded and crossfolded into a nonwovenweb having a basis weight of 125 gm⁻² by the following method.

Fibre was fed through a Tathams Roller and Clearer card with five setsof workers—and strippers to form a card web at the doffer of 12 gm⁻².The card web was fed through an Interweb crosslapper to provide a10-layer structure and compressed by the action of a weighted roller atthe outlet to the crosslapper. Medical grade paper (which is a lowlinting and low shedding paper) was interleaved between the structure toensure that on wind-up there was no delamination of adjacent layers.

The crossfolded fabric was unwound and fed into a Fehrer single boardneedleloom with a lattice feed and a stainless steel bed and stripperplate. The alginate structure was supported on a 40 gm⁻² woven lyocellfabric (plain weave) made from 80's cotton count lyocell by John SpencerLtd (Burnley). Prior to the material being fed through the needleloomthe medical grade paper was stripped away.

The operating parameters of the needleloom were as follows:

Needle type: 15×18×38×3RBA, F20 6-3B (Foster Needles)

Needle punch density: 80 ncm⁻² (uniform distribution with herring bonearray)

Penetration: 10 mm

Needleboard stroke: 500 strokes per minute

Speed through loom: 2.5 m/min

Test Data:

The resultant needled composite fabric was tested with the followingproperties measured:

Basis Shrinkage Absorbency Absorbency Wet Tensile Weight (%) (g/g)(g/100 Strength Sample (gm⁻²) (i) (ii) cm⁻²) (N/cm) (iii) Standardsodium/calcium alginate 148 40.7 16.3 24.1 0.5 Reinforced sodium/calciumalginate 175 27.0 14.9 26.0 4.2

-   (i) Shrinkage is by area during the absorbency test:-   (ii) The test method used was as set out in the British    Pharmacopoeia-1993, addendum 1995, page 1706 in the section    describing alginate dressings, the section headed Absorbency.-   (iii) The test method used was as follows:    -   1. The fabric was cut in the cross-direction into strips each        measuring 10×2.5 cm.    -   2. An Instron 1122 tensile machine was set up under the        following conditions:—        -   B-cell        -   Yam jaws        -   Test length 5 cm        -   Cross head speed 10 cm/min        -   Full scale load 2 Newtons    -   3. The dry sample was placed into the jaws of the Instron        machine.    -   4. 2 ml of 0.9% sodium chloride was applied by syringe evenly        onto the fabric.    -   5. The sample was left for 1 minute.    -   6. The chart recorder was checked to ensure that it was zeroed.

1. A method for the manufacture of a reinforced gel-forming fabriccomposite having a reinforcing layer and gel-forming fibre material,comprising the step of needling the gel-forming fibre material innon-woven fabric form into the reinforcing layer from one side so as topenetrate through the reinforcing layer and form a layer of gel-formingfibre material on both sides of the reinforcing layer.
 2. A method asclaimed in claim 1, wherein the gel-forming fibre is alginate fibre. 3.A method as claimed in claim 2, wherein the alginate is a calciumalginate or sodium/calcium alginate.
 4. A method according to claim 3,wherein the gel-forming fibre material is formed by non-woven cardingand crossfolding of gel-forming fibre.
 5. A method according to claim 4,wherein the gel-forming fibre material is needled at a needle punchdensity of from 40 to 200 ncm⁻².
 6. A method according to claim 5,wherein the reinforced fabric is manufactured by a single pass through asingle-board needle loom.
 7. A method according to claim 6, wherein thereinforcing layer is selected from a group consisting of a wovencellulosic fibre layer, a non-woven cellulosic fibre layer, a knittedcellulosic fibre layer, and a synthetic fibre layer.
 8. A methodaccording to claim 7, wherein the reinforcing layer is selected from agroup consisting of a lyocell fibre layer, a nylon fibre layer, apolyester fibre layer, and a polyethylene fibre layer.
 9. A methodaccording to claim 8, wherein the reinforcing layer is sputtered, coatedor impregnated with silver prior to the gel-forming fibre being needledinto and through it.
 10. A method according to claim 1, wherein thegel-forming fibre material is formed by non-woven carding andcrossfolding of gel-forming fibre.
 11. A method according to claim 1,wherein the gel-forming fibre material is needled at a needle punchdensity of from 40 to 200 ncm⁻².
 12. A method according to claim 1,wherein the reinforced fabric is manufactured by a single pass through asingle-board needle loom.
 13. A method according to claim 1, wherein thereinforcing layer is selected from a group consisting of a wovencellulosic fibre layer, a non-woven cellulosic fibre layer, a knittedcellulosic fibre layer, and a synthetic fibre layer.
 14. A methodaccording to claim 13, wherein the reinforcing layer is selected from agroup consisting of a lyocell fibre layer, a nylon fibre layer, apolyester fibre layer, and a polyethylene fibre layer.
 15. A methodaccording to claim 1, wherein the reinforcing layer is sputtered, coatedor impregnated with silver prior to the gel-forming fibre being needledinto and through it.